A three-pole single throw switch with defected ground structure (DGS) is proposed. The equivalent circuit for the proposed switch structure is derived based on equivalent circuit of newly proposed DGS unit structure. The equivalent circuit parameters of DGS unit are extracted by using the circuit analysis method. The on/off aperation of the proposed switch is obtained by varying the capacitance in the ground metallic plane. The experimental results shows excellent insertion loss characteristic at on state and isolation characteristic at off state.